Sound does not persist, neither across space nor across generations, so the tremendous rattle of horse-drawn drays, the clink of cupboards, the sneezes and shuffles of domestic life fall into the vacuous, silent crevices of history. “How did diners respond to the switch from pewter to china?” Schwartz wondered aloud. “How did a midwife register the sound of a new baby coming into the world? How did a person walking out in the woods register the sound of thunder or lighting?”

In the course of nearly two decades of research, he had examined diaries, listened to wax cylinders, poured over digitized copies of the Brooklyn Eagle from 1901, and yet these subtle historical shifts in the soundscape eluded him.